Werner meier



Aug. 25, 1925.

w. MEIER MEANS FOR ELECTROMAGNETICALLY FIXING WORK PIECES Filed April 9, 1920 Patented Aug. 25, 1925.

UNITED STATES PATENT OFFICE.

WERNER MEIER, OF ZURICH, SWITZERLAND, ASSIGNOR, BY MESNE ASSIGNMENTS, TO

FIRMA. AKTIENGESELLSCHAFT J. ZEHNDER & SOI-INE, OF GRANICHEN, SWITZER- LAND.

MEANS FOR 'ELECTROMAGNETICALLY FIXING WORK PIECES.

Application filed April 9, 1920. Serial No. 372,441.

To all whom it may concern Be it known that I, WERNER MEIER, a citizen of the Republic of Switzerland, residing at Zurich, Bolleystrasse a0, Switzerland, have invented certain new and useful Improvements in Means for Electromagnetically Fixing Work Pieces, and I do hereby declare the following to be a clear, full, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same, reference being had to the accompanying drawings, and to letters or figures of reference marked thereon, which form a part of this specification.

This invention relates to means for electromagnetically holding work pieces. The electromagnetic plates or chucks used heretofore for holding work pieces for instance in grinding machines, are worked with direct current. As a rule alternating current is used in work shops for lighting and driving purposes, therefore the use ofa direct current magnet plate necessitates either a direct current generator or a converting of alternating current into direct current, for instance by means of a rotary convertor. The use of electromagnets excited by alternating current would bring the important advantage of enabling the utilization of alternating current directly for magnetizing without having to transform it first into direct current.

The object of the present invention is an electromagnetically operated chuck where in at least two magnets magnetized by alternating current are used beside each other.

In using alternating current directly for magnetizing purposes to generate large pulling forces the following difficulties present themselves:

a. A vibration of the work piece takes place caused by the pulsations of the current;

I). The pulling force is not constant;

0. A heating up of the work piece to be held takes place originating from the hysteresis from eddy-currents and short circuitcurrents.

Fig. l of the accompanying drawings illustrates by way of a diagram the pulling force of an alternating current magnet in which i is the instantaneous value of the alternating current, B the induction and Z the pullling force. The relation of these values is expressed in the equations BzaEzcz' further Z- -cB in which 0, 0' and c are constants. As the pulling force is in proportion to the square of the induction, it is always positive if the latter is not equal to zero.

It results from the foregoing that the pulling force is equal to zero at certain intervals and it is therefore possible that the piece of work can shift during these intervals. In'order to do away with this principal disadvantage of the alternating current magnets, the magnetizing currents of the alternating current magnets are chosen so that a difference of phases exists between them. In consequence thereof the pulling forces of both magnets do never at the same time become equal to zero, i. e. a pulling force is always exerted byone of the magnets. This arrangement presents moreover the advantage that the vibrations disappear.

The difliculties mentioned above sub a and Z) are overcome in this way. 1

In the case of single phase current. two magnetic circuitswith a difference of phases may be obtained in inserting into one of the circuits induction coils and in saturating the two circuits unequally.

The E. M. F. of self-induction, on which the arrangement principally depends is:

irfiLliEii. 10 Z (ZH (it wherein s is the number of turns, 9 the cross-section, Z the average length of the magnetic circuit, B the induction, H the intensity of field, c the instantaneous value of the current and the fluxes oi? the out-of-phase magnetic circuits. The vectors rotate around point 0, the projections of the three phases onto line NN Show the instantaneous values of the fluxes. The pulling; force is proportional to the square of the fluxes. Further it in be seen from the vector-diagram that the fluxes are never equal to zero and thereitz the pulling force can never be equal to zer It the n'iagnetic cores were maximally satu 'ated, a large work piece would be con siderably heated up by the eddy and hysteresis-currents. Preferably the are only slightly saturated and B has to be chosen to 3000-10000 lines, whereupon only a slight heating-up takes place. With such a small saturation large and small work pieces are attracted with the same pulling force because the pulling force per square centimeter is small with large work pieces but the surface is whereas with small work pieces the pulling force per square centimeter is very large, because all the lines of force ot the magnet are concentrated over a small surface. Thus the same pulling force is attained as for a large work pi ce.

On the accon'ipanying drawings the exemplitications oi? the invention are shown:

Fig. 3 shows one mode oi carrying; out the invention partly in front View partly in rev tical section.

F 4t is a plan of Fig. 8.

Fig. 5' is a side view partly shown in section.

Fig. 6 shows a diagram of connections.

Fig. 7 is a diagrannnatic sketch.

The cores 1., 2, 4t, 5, 0 of the nie't-inet consisting o't 'licon dynamo sheets are connected in pairs to a yoke 7. Coils 8 are sit a, 5. G th ampereuated. on the cores 1, 9, 3, turns of which produce the magnetic lines of force. Each magnet is screwed by men is of brass scr ws 9 to a chucl: base plate 10 of iron. cast-iron (5 inch ilralne ll is niounted on the bmieplate brass tacings 1.2 are arrangg f hetv'eer tranie Ill. and the magnets row the purpose of :nagrnetic insulation. v tween the tree ends chuck inn.

o'f tibre 13 are l core bar mi ed for sulatingr hein electrica at magnetically. The uuig'netic circuits are cloned. by means ot a work pie e shown 1: F g. 3 in dotted lines ant. the fibre bars l3 pr a dir the magnetic lines from one were t0 the nerd. The who apparatus nclosed by chuck cover. 14 ot z .nnnun'i.

strated serves me work in mea in are connected up so that three phase alterr tin e current may be used for working); same. To this end the magnet coils S are connected to a plug): de vice 15 with which they are electrically coui'zected in a manner shown diagrannnatically in Fig. 6. The chuck cores 1, 2, 3, 4-, 5, 6

The electromagnetic chuc principally for holding chine tools 1 its coil orn: three i .tnteu magnetic circuits each oili which by one of the p'az The other the apparatus shown in Fig. :5 1s

s .ed as the one above djaceut iuagraets coi prising "ZOQ'GtliiEl' a chuck pa e clei l: shown in :3 consists t v 3 plate elements arranged in one a. s. "We i'la'e elements lfor altwnatnug current n'n also be arranged beside each over the pine device is arraut; d so and the coils are connected up to it in such a way that possible to connect the coils 8 of magnet cores 1. 2, 3, l, 5, (5 in star L llwo adjacent magnets e theretor'e led with out-o't-phase currents.

user-trip a three-pole plus; into one or the 0 set of holes 1.0 and 17 staror deltaconnectiou produced. li hen such a plug nsertcd into the upper three holes the aguct cois connected in star conuection when is inserted into the holes t7 the coils are in delta cminection. The plug devices are connected electrically with theplugz holes 18 adapted to be conueced to a power main. The pull' i force varies in accordance with the connection made a QLJZ :0.ll the pulling 'lorccs are theoretically in a 'atio of l :3.

' device for holdpieces electroinaanetic: lly by rect ci' zrent in which the mate insulated magnetically l'roiu y means at zinc bars. hese nine 0 used. with alteri'uitiup; current c tit-(wrrenls would b generated 1 r ild act as slnirt'circuit d a tiauislornier as shown in 'l hcsc iort circuit currents would generate much heat and. the device would he- U1 contradistinctimi to a and they 5% ol the total ur may be taken to be netic flux. la the drawing! the pole-shoes are ct an elon 'atcd. shape whereby the phases are arranged nearer to each other.

\ ice for fixing work pieces may three, six, nine etc. magnetic circhuck comprising an oblong chuck base plate, a frame extending around the edges of said plate, a metallic magnetic insulator seated in said frame, narrow, spaced, laminated magnetic cores mounted on said insulator, said cores arranged transversely of the longitudinal axis of said plate and frame, screws passing through said plate and engaging said cores to hold them on said insulator, a solid insulating material filling the spaces between the outer ends of said cores and forming with the outer ends of the cores a plane chucking face, windings on said cores for alternating current, means to differently connect the windings to change the holding power of the chucking face, and a casing between said base plate and chucking face, said base plate, casing and chucking face connected water-tight.

In testimony that I claim the foregoing as my invention, I have signed my name.

WERNER MEIER. 

